Star Constellation Facts: Draco

Draco depicts a dragon, with the creature’s head located just north of Hercules, and its tail ending between the big and small dippers in Ursa Major and Ursa Minor respectively. It takes up an area of 1,083 square degrees of the celestial globe, making it the 8th largest constellation in the night sky, and being circumpolar is visible to most observers in the northern hemisphere right through the year. The constellation can also be seen from latitudes as far south as -15 degrees.

The most notable deep sky objects in Draco are the Cat’s Eye Nebula, and the Tadpole Galaxy, and while Draco contains nine known stars with planets, the constellation contains only one Messier object, namely the Spindle Galaxy (M102).

Ursa Major Family of Constellations

Draco is also part of the Ursa Major family of constellations, together with the constellations Coma Berenices, Boötes, Camelopardalis, Canes Venatici, Corona Borealis, Leo Minor, Lynx, Ursa Major and Ursa Minor.

Mythology

Although Draco has several associated myths, perhaps the most famous is the Greek myth in which it represents Ladon, the dragon tasked by Hera with guarding the golden apples in the Garden of the Hesperides. The apples in the orchard were grown from the wedding gift given by Gaia to Hera and Zeus, and Hercules eleventh labor involved stealing three Golden Apples from this dragon guarded tree.

Meteor Showers

Only one meteor shower, the Draconids, is associated with the constellation, and is the result of the Earth passing through the dust trail of comet 21 P/ Giacobini-Zinner. The Draconids usually peak in the second week of October, and although this shower is usually described as “unspectacular”, and “hardly worth watching”, with some luck the next Draconids shower will be as spectacular as the one seen in 2011.

Notable Stars

– Kepler-10, although not one of the most luminous stars in Draco, is notable for the fact that it was the first star identified by the Kepler telescope as having at least two planets. The first planet, Kepler-10b, is a small rocky planet that orbits its G-class parent star every 0.8 days, while the second planet, Kepler-10c, has an orbital period of 42.3 days, placing both planets too close to the parent star to host life. At an estimated age of around 11.9 billion years, Kepler-10 is more than twice as old as the Sun, and at an apparent visual magnitude of 10.69, it is invisible without optical aid.

– Etamin (Eltanin, Gamma Draconis), at an apparent visual magnitude of 2.36, and a distance of about 154 light years, is the most luminous star in Draco. It is also referred to as the Zenith star because it lies almost directly overhead as seen from London. An evolved giant star (K5 III), Etamin is 471 times as luminous as the Sun, even though it is only 72% more massive. It is also orbited by a suspected red dwarf with a magnitude of 13.4.

Etamin derives its original name from the Arabic word At-Tinnin, which roughly translates into “great serpent”. Look for Etamin to the north-north-westward of Vega, the most luminous star in the constellation Lyra. Another notable feature of Etamin is the fact that its proper motion will bring it to within 28 light years of Earth in about 1,500 million years, which will make it as bright as Sirius is today- if we were around to see it.

– Aldibain (Eta Draconis) is 92 light years away, and has an apparent visual magnitude of 2.73, making it the second most luminous star in Draco. Classified as a G8 III star, it is 60 times as bright as the Sun, about 550 million years old, and it is orbited by a companion star at a distance of 5.1 arc seconds. The companion is a K2-V main sequence star with an apparent magnitude of 8.8, and its orbital period is at least 1,000 years.

– Rastaban (Beta Draconis), about 380 light years away, is the third most luminous star in Draco with an apparent magnitude of 2.79. Classified as a G2 bright giant, Rastaban is about six times as massive as the Sun, about 40 times as big, and a spectacular 950 times as bright. It is also the primary component of a binary system, with the other component being a dwarf star. Rastaban’s name derives from the Arabic ra’s ath-thu’ban, which roughly translates into “the head of the serpent.”

– Altais (Delta Draconis), another notable bright star in Draco, is a G9 III star that is 97 light years away, 59 times as luminous as the Sun, and has an apparent magnitude of 3.07. It is estimated to be about 800 million years old, and it name derives from the Arabic Al Tais, which translates into “the goat.”

Notable Deep Sky Objects

The Cat’s Eye Nebula (NGC 6543) has an apparent magnitude of 9.8, and is about 3,300 light years distant. It is also one of the most complex nebulae ever discovered, with its many concentric shells of gas and dust being the subject of intense study by astronomers. The nebula formed about a thousand years ago when the central star, that is at least 10,000 times as bright as the Sun, blew off an envelope of material. It is thought that the central star is in fact a binary system, and that the interactions between the stars in the system is what causes the highly complex arrangement of the inner shells. What is known however, is that the very powerful solar wind of the central star is blowing off about 20 trillion tons of stellar material per second, which is why the star is now believed to be only a little more massive than the sun.

Spindle Galaxy (Messier 102, NGC 5866); it is not certain who discovered this galaxy first; both Charles Messier and Pierre Méchain are credited with the discovery, but it is certain that William Herschel discovered it in dependently in 1788. Although the galaxy is either a spiral, or lenticular galaxy, its shape resembles that of a spindle or rod, hence the name, since we see it exactly edge-on. The dark dust ring around the galaxy may not be a strange feature for a spiral galaxy, but it is highly unusual in lenticular galaxies. However, since the issue of the galaxy’s shape is far from being decided one way or the other, the presence of the dust ring will remain a mystery.

Abell 2218 is a galaxy clusters that has the distinction of having being used as a gravitational lens to track down the oldest known object in the universe, a 13-billion year old galaxy that is thought to have formed as soon as 750 million light years after the Big Bang. Abell 2218 is larger than most galactic clusters, and due to its mass of about 10,000 galaxies, the light that passes by it is curved and then refocused in front of it, which is how objects vastly further away become visible. The several arcs in this image is light that was bent by the clusters’ mass, and each arc represents the light from an object behind the cluster, which is only about 2.3 million light years away. The arcs of light in this image, also known as “Einstein Rings”, can be analyzed in the same way that the light from an undistorted image can be analyzed, which is how the oldest known object in the Universe was identified.

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